Help With discount

[#1]

Hi can someone help me i have an order form and i trying to do discount section. I want to do something like if client type by example SALE in Promo Code the Total Net value will go down by 5%. Any help or idea would be great. Thanks

[#2]

HI there,

Promo Code Field : txtPromoCode

% Discount Field : txtDiscount (can be hidden)

Total € Field : txtTotal

Hope this will help!